Conventionally, technologies disclosed in the patent documents 1 and 2 are known as a force sensing device.    Patent document 1: JP-H09-128142A    Patent document 2: JP-H10-197373A
In the technology disclosed in the patent document 1, a first strain detecting plate and a second strain detecting plate both of which have elasticity are combined in a cross shape in a plan view. The combined first and second strain detecting plates are disposed on a base plate so as to be placed vertical to the surface of the base plate. Strain gages are arranged on the surfaces of the first and second strain detecting plates. The strain gages have strain sensitive axis corresponding to directions perpendicular to longitudinal directions of the strain detecting plates.
In the technology disclosed in the patent document 2, the device includes an elastic plate which has elasticity, a manipulatable member and a set of four strain detecting elements, i.e., strain gages. The manipulatable member is disposed on the center of the elastic plate. At least a lower part of the manipulatable member is made of an elastic metallic wire. The strain detecting elements detects deformations of the elastic plate.
In the technology disclosed in the above-mentioned patent document 1, the surface of the base plate provides an X-Y plane and a direction vertical to the base plate provides a Z-axis. Since the first and second strain detecting plates have elasticity, the first and second strain detecting plates are distorted according to not only an applied force along an X-axis and a Y-axis, but also an applied force caused by a rotating moment about the Z-axis. Therefore, according to the technology disclosed in the above-mentioned patent document 1, it is possible to detect the applied forces of three degrees of freedom which includes force acting along the X-axis, force acting along the Y-axis, and force acting about the Z axis caused by a rotating moment. However, the technology in the patent document 1 requires employing a plurality of surfaces in order to support the strain gages, i.e., both surfaces on the first and second strain detecting plates are used for supporting the strain gages. Therefore, it is required to take complicated wiring steps, i.e., a soldering step, for leading out wirings from the strain gages. This may cause increase of cost.
On the other hand, in the technology disclosed in the patent document 1, since all of four strain detecting elements are disposed on the same surface of the elastic plate, wiring can be easily taken out from the strain detecting elements. In the technology disclosed in the patent document 2, the surface of the elastic plate provides an X-Y plane and a direction vertical to the elastic plate provides a Z-axis. Since elastic member is a flat plate with a rectangular shape in a plan view, even if a rotating moment about the Z-axis is applied, an amount of displacement of the elastic plate caused by the rotating moment is extremely small. Therefore, it is difficult to detect distortion of the elastic plate which originates in the rotating moment about the Z-axis. Therefore, the device can detect only the applied forces of two degrees of freedom which includes the force acting on the Y-axis direction and the force acting on the X-axis direction.